The present invention relates to an antenna device for receiving a satellite signal transmitted from an artificial satellite and, more particularly, a structure gasket for waterproofing the antenna device.
Various antenna devices for receiving the satellite signal transmitted from the artificial satellite are proposed. As such antenna device, the GPS antenna device for receiving the GPS signal transmitted from the earth orbiting satellite, the SDARS antenna device for receiving the SDARS signal transmitted from the SDARS satellite, etc. can be exemplified.
The system for receiving the signal waves transmitted from a plurality of artificial satellites orbiting the earth, respectively by the receiver and then detecting a present position of the receiver itself based on information contained in the received signal waves, i.e., the Global Positioning System, is spreading recently. Commonly this system is called the GPS (Global Positioning System) in many countries such as Japan, the USA, etc. Also, commonly such system utilizes the GPS satellites that the Department of Defense of the USA manages. As the similar system, there are “GALILEO” utilized in Europe, “GLONASS” utilized in Russia, and the like. For convenience, the positioning system using the artificial satellite, the artificial satellite used in this positioning system, the signal wave transmitted from this artificial satellite, the receiver for receiving this signal wave, etc. are referred herein to as the GPS, the GPS satellite, the GPS signal, the GPS receiver, etc. respectively.
The GPS can detect the present position of the GPS receiver itself in substantially real time with high precision. For this reason, the GPS is used mainly in such an application that the GPS receiver is installed into a mobile body such as an automobile, an aircraft, a mobile phone, or the like, for example, to measure the present position of this mobile body.
At present, the GPS receiver suitable for the automobile, the so-called onboard GPS receiver, is rapidly spreading. In installing the GPS receiver into an automobile, a GPS receiving antenna device for receiving the GPS signal is set up to an outside of the automobile such as a roof, or the like, for example.
The SDARS (Satellite Digital Audio Radio Service) is the service provided by the digital broadcast utilizing the satellite (referred to as the “SDARS satellite” hereinafter) in the United States. That is, the digital radio receiver that can receive a satellite wave transmitted from the SDARS satellite or a terrestrial wave to listen to the digital radio broadcast is developed in the United States, and put to practical use. At present, in the United States, two broadcast stations, XM and Sirius, provide the radio programs on 250 channels or more in total throughout the country. Usually this digital radio receiver is installed into the mobile body such as the automobile, or the like, and can catch the radio broadcast by receiving a radio wave whose frequency is in about 2.3 GHz band. That is, the digital radio receiver is the radio receiver that can catch the mobile broadcast. Since a frequency of a receiving radio wave is about 2.3 GHz band, a receiving wavelength (resonance wavelength) λ at that time is about 128.3 mm. Here, the terrestrial wave is produced by receiving the satellite wave by the earth station once, then shifting slightly a frequency of the satellite wave, and then retransmitting the wave as a linearly polarized radio wave. In other words, the satellite wave is a circularly polarized radio wave whereas the terrestrial wave is the linearly polarized radio wave.
The XM satellite radio antenna device receives the circularly polarized radio wave from two stationary satellites, and receives the linearly polarized radio wave via the ground linearly polarizing equipment in the dead space. In contrast, the Sirius satellite radio antenna device receives the circularly polarized radio wave from three earth orbiting satellites (synchronous type), and receives the linearly polarized radio wave via the ground linearly polarizing equipment in the dead space.
In this manner, since the radio wave whose frequency is about 2.3 GHz band is used in the digital radio broadcast, in many cases the antenna device for receiving this radio wave is set up outside the room. Therefore, upon installing the digital radio receiver into the mobile body such as the automobile, or the like, the antenna device is attached to the outside of the automobile such as a roof, or the like of the mobile body.
Various antenna devices for receiving the satellite signal transmitted from the artificial satellite are proposed. For example, Patent Document 1 discloses the antenna device in which the gasket can be positioned easily with respect to the top cover.
Also, Patent Document 2 discloses the antenna device which causes an assembly thereof to be easy.
Such an antenna device 10 that is disclosed in Patent Document 1 and Patent Document 2 will be explained below with reference to FIG. 1. The illustrated antenna device 10 is the GPS signal receiving antenna device.
The antenna device 10 includes an antenna case 13, an antenna module 14, a gasket 15, and a signal line 16 which is a coaxial cable. The antenna case 13 is constructed by joining a dome-shaped top cover 11 and a bottom plate 12. The antenna module 14 is accommodated in the top cover 11. The gasket 15 is provided to a joined portion between the top cover 11 and the bottom plate 12 to ensure a sealing property of the antenna case 13. In this case, the gasket 15 is also called the waterproof packing because this member established a waterproofing. The signal line 16 is connected to the antenna module 14.
The antenna module 14 has an antenna element 20 and a circuit board 21. An antenna for receiving the GPS signal transmitted from the GPS satellite is formed on the antenna element 20. A circuit for applying various signal processes such as amplification of the GPS signal received by the antenna element 20 (referred to as a “signal processing circuit” hereinafter) is formed on the circuit board 21. The antenna element 20 and the circuit board 21 are joined mutually with a double-sided tape 22.
The signal line 16 for supplying the GPS signal to the outside of the antenna case 13 is connected to the circuit board 21. Also, a shield case 24 for shielding the signal processing circuit is attached to a main face of the circuit board 21, which is opposite side to the side on which the antenna element 20 is arranged. The signal line 16 is led out through a notched portion formed in the top cover 11 (described later).
The antenna device 10 is integrated when the top cover 11 and the bottom plate 12 are secured mutually by three screws 26 in a state that the antenna module 14 and the gasket 15 are accommodated in an internal space of the top cover 11.
The gasket 15 is made of a resin material such as silicon rubber. The gasket 15 has a base portion 15a for covering the whole face of the antenna module 14, and a gasket portion 15b for covering an outer periphery of the signal line 16 in a position that corresponds to a notched portion 11a (FIGS. 3A to 3C) formed in the top cover 11.
A configuration of the gasket 15 will be explained below in more detail with reference to FIGS. 2A to 2G.
The base portion 15a has a recess portion 15c. The position of antenna module 14 is regulated by this recess portion 15c. A shape of the recess portion 15c is formed to cover substantially the overall bottom face of the antenna module 14.
The gasket 15 is set between the top cover 11 and the bottom plate 12 when the top cover 11 and the bottom plate 12 are joined, and is provided for the purpose of ensuring the airtightness at the joining portion. The gasket portion 15b is formed upright on the base portion 15a in a position that corresponds to the notched portion 11a formed in the top cover 11. The gasket portion 15b has a hole portion 15d, through which the signal line 16 is passed, in its center portion.
The gasket 15 has a projection 15e that extends outward from the lower side of the hole portion 15d. This projection 15e constitutes a waterproof structure when this portion is brought into contact with the lower side of the signal line 16. The projection 15e is provided to expose from the notched portion 11a of the top cover 11, and constitutes a part of the face of the antenna main body. Also, the gasket 15 has four projections 15f provided to the lower face of the base portion 15a. These projections 15f pass through the bottom plate 12 and a resin sheet 31, and are exposed from the bottom face of the antenna main body. These projections 15f serve as a slip stopper when the antenna main body is set on the roof of the automobile.
Returning to FIG. 1, a single concave portion 12a is formed on a center portion of the bottom plate 12. A permanent magnet 30 is attached into the concave portion 12a. This permanent magnet 30 is provided to attract and fix the antenna device 10 onto the roof of the automobile. Also, the resin sheet 31 for the purpose of preventing a scratch on the roof of the automobile is attached onto the main face on the side, which faces to the outside of the bottom plate 12, over the almost whole part of this main face. The model number, the name, etc. of the antenna device 10 are printed on this resin sheet 31.
A configuration of the top cover 11 will be explained below with reference to FIGS. 3A to 3C.
The top cover 11 has a container portion 11c that is encircled with a substantially rectangular waterproof rib 11b. The container portion 11c accommodates the box-shaped antenna module 14. Also, protrusions 11d are provided integrally with a top face of an inner wall of the top cover 11 at four locations in the container portion 11c. These protrusions 11d are provided in the positions that contact the areas near four corners of the antenna element 20.
Also, the top cover 11 has a gasket receiving portion 11e for receiving the gasket portion 15b of the gasket 15, and three threaded holes 11f into which the screw 26 is screwed respectively.
As shown in FIG. 3C, an outer peripheral edge of an end portion 11b-1 of the waterproof rib 11b is chamfered. The end portion 11b-1 of the waterproof rib 11b is brought into contact with the gasket 15 when three screws 26 are screwed.
Also, twelve reinforcing ribs 11g are formed around the waterproof rib 11b of the top cover 11. The reinforcing ribs 11g are arranged to correspond to a shape of the gasket 15. In other words, a virtual shape formed when ends of the reinforcing ribs 11g are connected assumes such a shape that corresponds substantially to the shape of the gasket 15.
Therefore, as shown in FIGS. 4A and 4B, a position of the gasket 15 can be defined easily with respect to the top cover 11. As a result, workability in assembling the antenna device can be improved. In this case, the gasket 15 and the bottom plate 12 are secured to the top cover 11 by three screws 26, as described above. Therefore, unlike the state shown in FIGS. 4A and 4B, actually an upper outer peripheral edge of the gasket 15 is brought into contact with right-angled corner portions of the reinforcing ribs 11g by screwing pressure given by three screws 26.
Also, as shown in FIG. 3A, a grid-shaped rib 11h is formed on the inner wall top face of the inner wall of the top cover 11. Accordingly, a rigidity of the top cover 11 can be improved. The grid-shaped rib 11h is formed on a top face of an inner wall of the container portion 11c, which is encircled with the waterproof rib 11b, over the whole area except a square area including an almost center portion. This almost center portion in which the grid-shaped rib 11h is not formed is constructed such that power feeding pins protruded toward a receiving face side of the antenna element 20 are positioned therein. That is, the almost center portion serves a clearance for the power feeding pins when the antenna element 20 is contained in the container portion 11c. 
A configuration of the bottom plate 12 will be explained below with reference to FIGS. 5A to 5D.
A single concave portion 12a is formed in the center portion of the bottom plate 12. The permanent magnet 30 is provided in the concave portion 12a. The permanent magnet 30 is provided to attract and fix the antenna device 10 to the roof of the automobile. The bottom plate 12 has four through holes 12b through which four projections 15f of the gasket 15 are passed. Also, the bottom plate 12 has three holes 12c through which the screw 26 is passed respectively.
As shown in FIG. 1, a resin sheet 31 for protecting the roof of the automobile from scratch is attached onto the main face on the side, which faces to the outside of the bottom plate 12, over the almost whole face of this main face. The model number, the name, etc. of the antenna device 10 are printed on this resin sheet 31.
A combined state of the bottom plate 12 and the gasket 15 is shown in FIG. 6. As shown in FIG. 6, a diameter of the through holes 12b formed in the bottom plate 12 is larger than a diameter of the projections 15f of the gasket 15.
A length of the projections 15f is set short to such an extent that, even when the projections 15f are elastically deformed in the lateral direction, the projections 15f do not contact the corner of the through holes 12b. Also, as shown in FIGS. 2A to 2G, top end portions of the projections 15f are rounded.
According to such configuration, even when the projections 15f are elastically deformed in the lateral direction, the projections 15f of the gasket 15 never come into contact with the corner of the through holes 12b in the bottom plate 12. Therefore, the projections 15f can escape into the through holes 12b in the bottom plate 12, and thus the workability in assembling the antenna can be improved.    [Patent Document 1] Japanese Patent Publication No. 2006-237917A    [Patent Document 2] Japanese Patent Publication No. 2006-245719A
In the conventional antenna device 10, as shown in FIG. 3A, the waterproof rib 11b is provided on the inner side apart from the case side face of the top cover 11. In other words, a plurality of reinforcing ribs 11g are provided between the waterproof rib 11b and the case side face of the top cover 11. A dead space is formed in the top cover 11 because a plurality of reinforcing ribs 11g are provided. Therefore, the conventional antenna device 10 is increased in product size.
Also, as shown in FIG. 4A and FIG. 6, in the conventional antenna device 10, a plurality of screws 26 used to secure the gasket 15 and the bottom plate 12 to the top cover 11 are screwed into the threaded holes 11f of the top cover 11 in the positions that do not pass through the gasket 15 and are in close vicinity of the gasket 15. Therefore, in the conventional antenna device 10, the waterproof property in the inside of the antenna module 14 is ensured only by virtue of the close contact between the waterproof rib 11b provided to the top cover 11 and the gasket 15. As a result, the waterproof is not sometime enough.
As shown in FIG. 11A, in the conventional antenna device 10, when three screws 26 are screwed into three threaded bosses 11f of the top cover 11 through the holes 12c in the bottom plate 12, the gasket 15 is set between the top cover 11 and the bottom plate 12 and is fixed by the screws. Therefore, in the conventional antenna device 10, the waterproof property in the inside of the antenna module 14 is ensured only by virtue: of the close contact between the waterproof rib 11b provided to the top cover 11 and the gasket 15. As a result, such a problem exists that the waterproof is not enough.